Modern day one of the best pound for pound fighters of the world Sergio Martinez started at 19 I think or 20. Also Bernard Hopkins and Wilfredo Velasquez at 18.

Archie Moore started pro boxing in 1938 at 25 years old and won the light heavyweight championship in 1952 at age 39.

The "Old Mongoose" was 23 at most when he started fighting for money (he claimed to have been 20).

Rocky Marciano and "Tiger" Flowers both started late.

Boris Shultz of Germany started boxing at 52 AND WON title at age 54....

I just answered this.....Sergio Martinez started boxing at 20.